1. Field of the Invention
The present invention relates to a rotator element for an electric motor. More particularly, the present invention relates to an improved rotator element having permanent magnets.
2. Description of the Related Art
A conventional rotator element for an electric motor is shown in FIG. 1, which is similar to the permanent magnet: type of the rotator element disclosed in the Japanese Patent Disclosure 60-109749. As shown in FIG. 1, rotator element 2 has a cylindrical core body 4 made of stacked iron disc-shaped plates 8 and a plurality of permanent magnets 6 secured to cylindrical core body 4. Each of the disc-shaped plates 8 has cutout portions on its circumferential area. The cutout portions make holes for inserting magnets 6 when disc-shaped plates 8 are stacked. Permanent magnets 6 with opposite poles are alternately inserted in the holes. Disc-shaped plates 8 are firmly fastened between lid plates 30 with rivets 32.
In order to perform the smooth insertion of magnets to core body 4, each of magnets is provided with a cutaway portion 26 at their ends adjacent the lid plates 30 as disclosed in FIGS. 2, 3a and 3b. Cutaway portion 26 provides a clearance between the magnet 6 and the disc-shaped plates 8 which contain them. The clearance serves for the smooth insertion of magnets 6 into the holes without deforming or cracking the magnets 6, however it causes a disadvantage. As illustrated in FIG. 2, a cylindrical surface of core body 4 is shaped with a cutting tool 40 such as a bite for developing a uniform air gap of the motor, which would realize a suitable magnetic field in the air gap. When cutting force is applied to stacked disc-shaped plates 8 in the area of cutaway portions 26, disc-shaped plates in areas L1 and L2 are displaced or moved as shown in FIG. 3a or FIG. 3b. Such displacement causes the deformation of disc-shaped plates 8 and the dimensional inaccuracy of core body 4.